Water quench and tar remover for cracked gases



y 29, 1956 o. KILPATRICK 2,747,680

WATER QUENCH AND TAR REMOVER FOR CRACKED GASES Filed March 10, 1952QUENCHED 8. PURIFIED GAS INVENTOR.

MYRON O. KILPATRICK A ORA/E75 United States Patent WATER QUENCH AND TARREMOVER FOR CRACKED GASES Myron 0. Kilpatrick, Bartlesville, 0kla.,assignor to Phillips Petroleum Company, a corporation of DelawareApplication March 10, 1952, Serial No. 275,840 13 Claims. (c1. res-2This invention relates to gas purification. In one aspect, it relates tothe removal of tar from cracked gas. In another aspect, it relates to amethod and apparatus for absorption and scrubbing. In another aspect, itre lates to phase separation or skimming.

Hydrocarbon cracking is known to be accompanied by tar formation. Thepresence of tar in a cracking effiuent causes operating difliculties bydepositing in pipes, valves, blowers, etc. It is, therefore, desirableto remove the tar as soon as possible after the cracking step.

It is known to quench a cracked gas with water to cool the gas andelfect a partial removal of tar. Complete removal of tar is not thusobtained. It is also known to use an oil for quenching and tar removal.However,

most oils do not have the desirable heat-removing capacity that waterhas.

This invention provides the desirable quenching and tar removalproperties of both water and oil. It does so in a simple, unitary systemof apparatus, and effects an improved separation of oil, water, and tarfrom each other so that the oil and the water are readily available forrecycling to the quenching apparatus.

According to this invention, gas effluent from a cracking system iscontacted first with Water and then with oil in the same quenching zoneto remove an and quench the gas. The function of the Water is primarilyto cool the gas and scrub tar therefrom. The function of the oil isprimarily to cool the gas further and remove any remaining tar therefromby absorption or solution and scrubbing.

In a specific embodiment ofthe invention, the oil, the water, and thetar are removed from the quenching zone to a stratification zone, wherethe mixture stratifies into three phases, namely, an oil phase, a waterphase, and a tar phase. The tar phase is withdrawn from the system. Theoil and the water phases are separately recycled to the quenching zone.

In a further embodiment of the invention there is provided a quenchingand tar removal apparatus comprising a quenching zone, gas inlet meansin a lower part of said quenching zone, water introduction means in anintermediate part of said quenching zone, oil introduction means in anupper part of said quenching zone, gas withdrawal means at the top ofsaid quenching zone, liquid withdrawal means at the bottom of said zone,stratification means communicating with said liquid withdrawal means,means for separately recycling oil and water from said stratificationmeans to said quenching zone, and means for removing tar from saidstratification means.

In another embodiment of the invention there is provided astratification apparatus comprising a generally horizontal tank, oilskimming means in said tank, tar collecting means in said tank, oilwithdrawal means attached to said skimming means, tar withdrawal meansattached to said tank, and water withdrawal means attached to said tank.

The attached drawing illustrates one embodiment of the invention.

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The gas quenched according to this invention will ordinarily be a gaswithdrawn from a thermal cracking system such asa pebble heater. It willordinarily have been preliminarily quenched to a temperature in therange 500 to 1000 F. before entering the system illustrated in thedrawing.

The gas enters tower 2 through inlet 3 and passes upwardly through tower2. Water introduced through inlet 22 and cooler 18 passes to spray means5 in tower 2. The water counter-currently contacts gas in the tower,cools it and removes tar therefrom by scrubbing action. The gas whichhas been contacted with water passes up- Wardly through trays 4 and iscounter-currentlycontacted with oil introduced through inlet 21, cooler19 and onto the top tray in tower 2. The oil further cools the gas andremoves the last traces of tar therefrom by scrubbing and absorption orsolution. Cooled and scrubbed gas substantially free of tar is withdrawnthrough outlet 5 at a temperature in the range 50 to 200 F., preferablyabout F. The gas can be passed through condensing means 8 to removetherefrom by condensation any oil vapor remaining in the gas or it canbe bypassed through conduit 7 and withdrawn through outlet 9. Anycondensed material is returned to tower 2 through conduit 2t and inlet21.

A mixture of water, oil and tar is withdrawn from the bottom of tower 2and passed to settler 11. in settler 11 the mixture stratifies into anupper oil layer, intermediate water layer and lower tar layer. Oilcollects in skimming member 12, which is attached to the top of settler11 and which includes skimming member 12a and oil removal member 12b.The oil collected is removed through member 1212, conduit lS, and.conduit 17 and is recycled through inlet 21 to the top of tower 2. Ifdesired, part of the oil may be withdrawn through outlet 23, and passedto means not shown for purification i. e., removal of dissolved tar.Water is recycled through conduit 16, inlet ,22 and cooler 18 to spraymeans 5. Baffie 13 in settler 11 serves to separate tar from water byretaining the tar and not allowing it to enter recycle conduit 16. Taris withdrawn from the system through outlet 14 in the bottom of settler11. If desired, settler 11 can be provided with a conical or pyramidalbottom to facilitate collection and removal of tar. Certain tars containconstituents which are insoluble, in part, in aromatic solvents and havea higher specific gravity than Water (See Perry, Chemical EngineersHandboo second edition, 1941, N. Y., McGraw-Hill Book Co., Inc., page2375).

The oil used in the process of this invention is preferably an oil whichis predominantly aromatic. Examples of suitable oils are benzene,toluene, anthracene oil; predominantly aromatic kerosenes having, forexample, a boiling point in the range of 200 to 500 F; and apredominantly aromati-c gas oil, such as a gas oil recycled in acracking system and having a boiling range of 400 to 700 F. Thoseskilled in the art will recognize that most of the foregoing solventshave a specific gravity less than that of Water. When a solvent havingsuch a specific gravity is used, the embodiment shown in the drawingwill be utilized exactly as shown. However, those skilled in the artwill also recognize that certain anthracene oils have a specific gravitygreater than 1. (See: Thorpes Dictionary of Applied Chemistry, fourthedition, volume 3, page 211, Longmans-Green & Co., N. Y., 1939). Fromthe foregoing, those skilled in the art will recognize that when such anoil is used the relative positions of the oil and water layers in thestratification zone will be reversed with respect to that shown in thedrawing.

Variation and modification are possible within the scope of thedisclosure and claims to this invention, the essence of which is that agas from a cracking system can be.

cooled and tar removed therefrom by contacting first with water and thenwith oil and that the oil, the water and the tar obtained can beseparated from each other by stratification, the invention beingconducted in a unitary system of apparatus comprising a quenching towerand a stratification means.

I claim:

1. A process for quenching a cracked gas and removing tar therefromwhich comprises passing said gas upwardly through a quenching zone,contacting said gas with water in a lower part of said zone, contactingsaid gas with a predominantly aromatic oil in an upper part of saidzone, recovering a quenched and purified gas from an upper part of saidzone, removing a liquid mixture from a lower part of said zone, causingsaid mixture to stratify into an oil layer, a water layer, and a tarlayer, recycling said water layer and at least part of said oil layer tosaid quenching zone, and withdrawing said tar layer from the system.

2. The process of claim 1 in which said oil is benzene.

3. The process of claim 1 in which said oil is toluene.

4. The process of claim 1 in which oil is an anthracene oil.

5. The process of claim 1 in which said oil is an aromatic kerosene.

6. The process of claim 1 in which said oil is an aromatic gas oil.

7. The process of claim 1 in which said gas is initially at atemperature in the range 500 to 1000 F. and is quenched to a temperaturein the range 50 to 200 F.

8. Apparatus for quenching a gas and removing tar therefrom, saidapparatus comprising in combination: a gas-liquid contactor; gas inletmeans in a lower part of said contactor; gas outlet means in an upperpart of said contactor; water introduction means in an intermediate partof said contactor; oil introduction means in an upper part of saidcontactor; liquid withdrawal means in a lower part of said contactor;stratification means communicating with said liquid withdrawal means;means for separately recycling oil, and water from said stratificationmeans to said contacting means; and means for withdrawing tar from saidstratification means.

9. The apparatus of claim 8 in which said water introduction means is aspray means and in which the upper part of said contactor containsgas-liquid contacting trays.

10. Apparatus for separating water, oil, and tar by stratification,which comprises, in combination: a generally horizontal tank; liquidinlet means at one end of said tank; liquid collecting means attached tothe top of said tank and including two side wall members, a bottommember and a liquid withdrawal member in open communication with theinterior of said collecting means through said bottom member, one ofsaid side wall members being attached to the top of said tank and tosaid bottom member, and the other of said side wall members beingattached to said bottom member and extending upwardly to a level belowthe top of said tank, the latter side wall member being positionedintermediate the firstmentioned side wall member and said liquid inletmeans; a vertical baffle attached to the bottom of said tank; tarwithdrawal means connected to the bottom of said tank; liquid withdrawalmeans connected to the bottom of said tank; said bafiie being positionedbetween said liquid withdrawal means and said tar withdrawal means andadapted to prevent tar from entering said liquid withdrawal means.

11. A process for quenching a cracked gas and removing tar therefromwhich comprises passing said gas upwardly through a quenching zone,contacting said gas with water in a lower part of said zone, contactingsaid gas with an oil in an upper part of said zone, causing oil to flowdownwardly through the entirety of said zone and water to flowdownwardly through the entirety of said lower part of said zonerecovering a quenched and purified gas from an upper part of said zone,removing a liquid mixture from a lower part of said zone, causing saidmixture to stratify into an oil layer, a water layer and a tar layer,and recovering each of said layers separately.

12. Apparatus for quenching a gas and removing tar therefrom, saidapparatus comprising in combination: a gas-liquid contactor; gas inletmeans in a lower part of said contactor; gas outlet means in an upperpart of said contactor; water introduction means in an intermediate partof said contactor; oil introduction means in an upper part of saidcontactor; liquid withdrawal means in a lower part of said contactor;and stratification means communieating with said liquid withdrawal meansand comprising a closed container adapted to contain liquid, saidcontainer being in open communication with said liquid withdrawal meansat one end of said container, liquid collection means attached to thetop of said container and including two side wall members, a bottommember, and a liquid withdrawal member in open communication with. theinterior of said collecting means, one of said side wall members beingattached to the top of said container and to said bottom member and theother of said side wall members being attached to said bottom member andextending upwardly to a level below the top of said container, thelatter side wall member being positioned intermediate thefirst-mentioned side wall member and said liquid withdrawal means, avertical baffle attached to the bottom of said container and extendingacross said container to the walls thereof, tar withdrawal means at thebottom of said container, liquid withdrawal means connected to thebottom of said container, said vertical battle being positioned betweensaid liquid withdrawal means and said tar withdrawal means and adaptedto prevent tar from entering said liquid withdrawal means.

13. A process for removing tar from a gas, which process comprisesintroducing said gas into one end of a scrubbing zone, introducing waterat an intermediate part of said scrubbing zone and causing water thusintroduced to flow countercurrently to said gas, introducing oiladjacent the opposite end of said zone and causing thus introduced oilto flow countercurrently to said gas substantially throughout the lengthof said zone, withdrawing oil, water and tar at the end of said zoneadjacent the point of gas introduction, and withdrawing scrubbed gasfrom said zone at the end adjacent the point of oil introduction.

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11. A PROCESS FOR QUENCHING A CRACKED GAS AND REMOVING TAR THEREFROMWHICH COMPRISES PASSING SAID GAS UPWARDLY THROUGH A QUENCHING ZONE,CONTACTING SAID GAS WITH WATER IN A LOWER PART OF SAID ZONE, CONTACTNGSAID GAS WITH AN OIL IN AN UPPER PART OF SAID ZONE, CONTACTING OIL TOFLOW DOWNWARDLY THROUGH THE ENTIRETY OF SAID ZONE AND WATER TO FLOWDOWNWARDLY THROUGH THE ENTIRETY OF SAID LOWER PART OF SAID ZONERECOVERING A QUENCHED AND PURIFIED GAS FROM AN UPPER PART OF SAID ZONE,REMOVING A LIQUID MIXTURE FROM A LOWER PART OF SAID ZONE, CAUSING SAIDMIXTURE TO STRATIFY INTO AN OIL LAYER, A WATER LAYER AND A TAR LAYER,AND RECOVERING EACH OF SAID LAYERS SEPARATELY.